1. Field of the Invention
The present invention relates to a glass structure having a through-hole or a cavity and particularly to a glass structure produced by laser beam irradiation and a method for producing the glass structure.
2. Related Art
A glass structure constituted by a finely treated glass substrate is used as an optical component used in optical communication or as a micro lens incorporated in a display device. As a method for finely treating such a glass substrate, wet etching using an etching liquid such as hydrofluoric acid or dry etching such as reactive ion etching is heretofore used generally.
Wet etching, however, has a problem in management and disposal of the etching liquid. Dry etching has a problem that an etching apparatus, itself large in scale, is required because equipment such as a vacuum vessel, etc. is required. Moreover, there is also a problem that these etching methods are not efficient because a pattern mask or the like must be formed by a complex photolithographic technique.
On the other hand, direct treatment using a physical change such as heating, melting, vaporization or ablation generated in a material irradiated with a laser beam has been developed. Reduction in laser beam width and wavelength has been achieved with the advance of laser technology. An organic substance such as polyimide or a metal has been machined in the order of microns. A laser beam is suitable for fine treatment because it can be converged to a very small light spot.
Glass is however apt to crack when machined because it is a brittle material. For this reason, it was not easy to use laser machining for the purpose of fine treatment. To solve this problem, a glass fine-treatment technique in which silver is imported into glass by ion exchange to reduce a threshold for laser machining to thereby restrain the glass from cracking etc. has been developed as disclosed in JP-A-11-217237.
In glass containing a large amount of alkaline metal, however, a phenomenon that diffusion of silver ions into the glass is disturbed because of reduction of silver ions in a limited region near surface of the glass occurs though silver ions can be imported into the glass by ion exchange. For this reason, an effective laser machining region is limited to a neighborhood of the glass surface. Accordingly, it is still difficult to process a glass substrate up to the inside of glass three-dimensionally with a high degree of freedom in such a manner that a through-hole is formed in the glass substrate and then the taper angle of a wall surface of the through-hole is further adjusted.
Even in the case where silver ions are not reduced in a neighborhood of the glass surface so that the silver ions can be diffused into the glass, the concentration of silver ions in the glass surface becomes always high because the silver ions must be imported into the glass through the glass surface by a diffusing process. Accordingly, treatment for a very long time is required for increasing the silver ion concentration in the inside of the glass to be approximately equal to that in the glass surface. Hence, there is a problem in production efficiency.